Such a method and apparatus requires that the video signal and at least one audio channel signal should be separately detected and that the detected video signal should have its luminance and chrominance components separated and separately treated, with the latter being shifted in frequency and otherwise treated to meet the requirements of the PAL color standard.
In my prior patent, U.S. Pat No. 4,148,077, a method is described for playing back black-and-white television signals for display at a slightly different line scanning frequency. By the system there disclosed, for example, television signals in accordance with the U.S. standard on a disc or a tape can be so played back that the signals picked up are suitable for a receiver designed in accordance with another standard, for example, Gerber standard. For this purpose it is necessary only to adjust the playback record speed (e.g., the rate of rotation of the turn table in the case of a disc record), so that the line-scanning frequency of the Gerber standard is provided in the reproduced signal.
Since the line-scanning frequencies of the two standards just mentioned lie very close to each other, the resulting picture field frequency with which the television receiver must be able to work varies only unsubstantially from the picture field frequency of the U.S. standard. In the case of modern television receivers, there is frequently no need whatever to get into the circuits of the receiver for modifications for such playback, since the range within which the deflection circuits can be synchronized can easily be, and often is, sufficiently wide so that the circuits can be synchronized to a picture field frequency of nearly 60 Hz, even though the receiver was intended to be used at the 50 Hz picture field frequency.
A more reliable operation is, nevertheless, obtained if the television receiver has switchable deflection circuits, with a switch position corresponding to each of the picture field frequencies to be used. It has been found that television signals recorded according to the U.S. standard can, in this way, be reproduced without difficulty in modern television receivers designed for use in accordance with the European television standard, but this success has, heretofore, been subject to the limitation that only black-and-white reproduction was involved. The different type of color encoding according to the U.S. standard (NTSC-standard) and the PAL standard utilized in most European countries permits no direct color reproduction, while American color television recording with European PAL television receivers.
It is an object of the present invention to provide a simple method and convenient apparatus by which it is possible to reproduce NTSC color television signals in television receivers equipped for reception of PAL signals, without the requirement of decoding and re-encoding the color signal.